In known screw conveyor devices of this type the internal core is arranged stationary in the housing, whereas the feed coil is mounted to be driven to rotate. In operation, excessive stress occurs between the relatively fast rotating feed coil and the stationary coil, causing both wear to the feed coil and core and damage to the conveyed material.
Furthermore, screw conveyor devices are known with one feed coil or even two driven feed coils disposed concentrically to one another, in which the central part is left free i.e. no core is provided. In screw conveyor device of this type there is often the disadvantage, particularly with conveyor device of considerable length and/or with material of high bulk weight being conveyed, that the necessary high torques and axial forces can be transmitted only to a limited extent. The result of this is that frequently in the case of particularly viscous and moist, products, the feed coils untwist or turn off and could break if the admissible strength is exceeded. Another disadvantage of these known screw conveyor devices is that with certain materials which are difficult to convey the speed of rotation has to be relatively high if the flowback of too much material through the central opening of the feed coil is to be avoided. However, particularly with screw conveyor device following a curved path, high speeds of rotation cause the feed coil to oscillate, especially if the conveyor device is insufficiently filled.
Finally, screw conveyor device for pourable material are also known which have a rigid feed screw. Conveyor device of this type have satisfactory conveying characteristics but they are suitable only for more or less horizontal and straight-line conveyance.